I don't understand that view. Care to elaborate?

Why shouldn't people use retarded as an insult? Because some handicapped people are retarded? Or is it that all handicapped people are retarded and retarded is just another word for it.

I always thought retarded means slow in the head to an degree that makes you not functional anymore. So a retarded person wouldn't be insulted by the word as they would be to retarded to comprehend the meaning.